Abstract: A mesomorphic compound represented by the following formula (I):R.sub.1 --A.sub.1 --B.sub.1 --A.sub.2 --R.sub.2 (I),wherein R.sub.1 and R.sub.2 respectively denote a linear or branched alkyl group having 3-18 carbon atoms capable of including one or non-neighboring two or more methylene groups which can be replaced with at least one species of --Z--, ##STR1## CH.dbd.CH-- and --C.tbd.C--, wherein Z denotes --O-- or --S-- and R.sub.3 denotes hydrogen or an alkyl group having 1-5 carbon atoms; B.sub.1 denotes ##STR2## A.sub.1 denotes a single bond, ##STR3## A.sub.2 denotes a single bond, --A.sub.3 -- or --A.sub.3 --A.sub.4 -- wherein A.sub.3 and A.sub.4 respectively denote any one of ##STR4## and Y.sub.1 and Y.sub.2 respectively denote any one of hydrogen, fluorine, chlorine, bromine, --CH.sub.3, --CN and --CF.sub.3.

Abstract: An optically active compound represented by the following formula (I): ##STR1## wherein R.sub.1 denotes an alkyl or alkoxy group having 1-18 carbon atoms; R.sub.2 denotes an alkyl group having 1-12 carbon atoms; A denotes ##STR2## X denotes and C* denotes an optically active asymmetric carbon atom. The optically active compound, when included as a component, provides a ferroelectric liquid crystal composition or device showing an improved electro-field response characteristic.

Abstract: A ferroelectric chiral smectic liquid crystal composition, comprising at least one compound represented by the following formula (I): ##STR1## wherein R.sub.1 and R.sub.2 respectively denote a linear or branched alkyl group having 1-8 carbon atoms capable of having a substituent; X.sub.1 and X.sub.2 respectively denote a single bond, ##STR2## Y.sub.1 denotes --CH.sub.2 O-- or --OCH.sub.2 --; and m and n are respectively 1 or 2; and at least one compound represented by the following formula (II): ##STR3## wherein R.sub.3 denotes a linear or branched alkyl group having 1-18 carbon atoms capable of having a substituent, R.sub.4 denotes a linear alkyl group having 1-10 carbon atoms; X.sub.3 denotes a single bond, ##STR4## Y.sub.

Abstract: A mesomorphic compound represented by the following formula (I): ##STR1## wherein R.sub.1 and R.sub.2 respectively denote a linear or branched alkyl group having 1-16 carbon atoms capable of having a substituent; Y.sub.1 denotes --COO--, --OCO--, --CH.sub.2 --or --OCH.sub.2 --; Z.sub.1 denotes a single bond, --O--, --COO--, --OCO-- or --OCOO--; and X denotes a halogen, cyano group or methyl group.

Abstract: A ferroelectric chiral smectic liquid crystal composition, comprising at least one compound represented by the following formula (I): ##STR1## wherein R.sub.1 denotes a linear or branched alkyl group having 1-18 carbon atoms capable of having a substituent; R.sub.2 denotes a linear or branched alkyl group having 1-14 carbon atoms capable of having a substituent; X.sub.1 and X.sub.2 respectively denote a single bond, --O--, ##STR2## m is 0-7; and n is 0 or 1; and at least one compound represented by the following formula (II): ##STR3## wherein R.sub.3 and R.sub.4 respectively denote a linear alkyl group having 1-18 carbon atoms and one --CH.sub.2 -- not bonded to X.sub.4 in the alkyl group can be replaced with --O--; X.sub.3 and X.sub.4 respectively denote a single bond, --O--, ##STR4## and p and q are respectively 0, 1 or 2 with proviso that both of p and q are not 0.

Abstract: A mesomorphic compound represented by the following formula [I]: ##STR1## wherein R.sub.1 and R.sub.2 independently denote an alkyl group having 1-16 carbon atoms capable of having a substituent; X.sub.1, X.sub.2, X.sub.3 and X.sub.4 independently denote a single bond ##STR2## A.sub.1, A.sub.2 and A.sub.3 independently denote ##STR3## X.sub.5 and X.sub.6 independently denote hydrogen atom, fluorine, chlorine, bromine, CH.sub.3, CN or CF.sub.3 ; n.sub.1 and n.sub.2 are 0 or 1, with provisos that (1) X.sub.2 cannot be a single bond when n.sub.1 is 0, (2) X.sub.3 cannot be a single bond when N.sub.2 is 1 and (3) at least one of X.sub.2 and X.sub.3 denotes ##STR4## when both n.sub.1 and n.sub.2 is O and A.sub.

Abstract: 1. A mesomorphic compound represented by the following formula 8 I]: ##STR1## wherein R.sub.1 and R.sub.2 respectively denote a straight chain or branch chain allyl group having 1-18 carbon atoms, wherein --CH.sub.2 -- in the alkyl group may be substituted by ##STR2## on condition that hetero atoms are not adjacent each other, R.sup.2 may be hydrogen atom, halogen atom, cyano group and trifluoromethyl group; n is 0 or 1, with the proviso that A.sup.1 denotes a single bond, ##STR3## when n is 0, A.sup.1 denotes a single bond when n is 1; A.sup.2 denotes any one of ##STR4## and X.sup.1, X.sup.2, Z.sup.1 and Z.sup.2 denote independently any one of hydrogen atom, halogen atom, cyano group and trifluoromethyl group, with proviso that X.sup.1, X.sup.2, Z.sup.1 and Z.sup.2 may not be all hydrogen atoms; Y denotes any one of ##STR5## a single bond.

Abstract: A ferroelectric chiral smectic liquid crystal composition, comprising at least one compound represented by the following formula (I): ##STR1## wherein R.sub.1 denotes a linear or branched alkyl group having 1-18 carbon atoms capable of having a substituent; X.sub.1 denotes a single bond, --O-- or ##STR2## Z denotes a single bond or ##STR3## denotes ##STR4## and n is an integer of 1-12; and at least one compound represented by the following formula (II): ##STR5## wherein R.sub.2 and R.sub.3 respectively denote a linear or branched alkyl group having 1-18 carbon atoms capable of having a substituent, at lease one of R.sub.2 and R.sub.3 being optically active; X.sub.2 and X.sub.

Abstract: A ferroelectric chiral smectic liquid crystal composition, comprising at least one optically active compound represented by the following formula (I): ##STR1## wherein R.sub.1 denotes a linear alkyl group having 1-14 carbon atoms; R.sub.2 denotes a linear or branched alkyl group having 1-14 carbon atoms capable of having a subtituent; and X.sub.1 denotes a single bond, ##STR2## and at least one compound represented by the following formula (II): ##STR3## wherein R.sub.3 denotes a linear or branched alkyl group having 1-18 carbon atoms capable of having a substituent; R.sub.4 denotes a linear alkyl group having 1-10 carbon atoms; X.sub.

Abstract: A mesomorphic compound represented by the following formula (I):R.sub.1 --A.sub.1 --B.sub.1 --A.sub.2 --R.sub.2 (I),wherein R.sub.1 and R.sub.2 respectively denote a linear or branched alkyl group having 3-18 carbon atoms capable of including one or non-neighboring two or more methylene groups which can be replaced with at least one species of ##STR1## wherein Z denotes --O-- or --S-- and R.sub.3 denotes hydrogen or an alkyl group having 1-5 carbon atoms; B.sub.1 denotes ##STR2## A.sub.1 denotes a single bond, ##STR3## A.sub.2 denotes a single bond, --A.sub.3 -- or --A.sub.3 --A.sub.4 -- wherein A.sub.3 and A.sub.4 respectively denote any one of ##STR4## and Y.sub.1 and Y.sub.2 respectively denote any one of hydrogen, fluorine, chlorine, bromine, --CH.sub.3, --CN and --CF.sub.3.

Abstract: A mesomorphic compound represented by the following formula (I): ##STR1## wherein R.sub.1 denotes a linear or branched alkyl group having 2-16 carbon atoms capable of including one or non-neighboring two methylene groups which can be replaced with --O--, --S--, --CO--, --COO-- or --OCO-- and capable of including a hydrogen atom which can be replaced with a fluorine atom; A denotes --A.sub.1 -- or --A.sub.1 --A.sub.2 --; B.sub.2 denotes --B.sub.3 -- or --B.sub.3 --B.sub.4 --; A.sub.1, A.sub.2, B.sub.1, B.sub.3 and B.sub.4 independently denote ##STR2## wherein Y.sub.1 and Y.sub.2 independently denote a hydrogen atom, F, Cl, Br, --CH.sub.3, --CN or --CF.sub.3, with the proviso that B.sub.1 can be a single bond; Z.sub.1 and Z.sub.2 independently denote a single bond, --COO--, --OCO--, --CH.sub.2 O-- or --OCH.sub.2 --; Z.sub.3 denotes --O--, --CO--, --COO-- or --OCO--; R.sub.2, R.sub.3 and R.sub.

Abstract: A mesomorphic liquid crystal composition stably exhibits lowered resistivity for quickly attenuating a reverse voltage caused by charge localization.

Abstract: A mesomorphic compound represented by the following formula (I): ##STR1## wherein R.sub.1 and R.sub.2 respectively denote an alkyl group having 1-16 carbon atoms optionally substituted; X.sub.1 and X.sub.3 respectively denote a single bond, --O--, ##STR2## X.sub.2 denotes a single bond, ##STR3## A.sub.1 denotes a single bond ##STR4## A.sub.3 denotes ##STR5## A.sub.2 denotes 9, 10-dihydro-2,7-phenanthrenediyl, 2,7-fluorenediyl or 2,7-fluorenonediyl; n is 0 or 1; and X.sub.4 and X.sub.5 respectively denote hydrogen, F, Cl, Br, --CH.sub.3, --CN or --CF.sub.3, with proviso that X.sub.1 is a single bond when A.sub.1 is a single bond.

Abstract: A mesomorphic compound represented by the following formula (I): ##STR1## wherein R.sub.1 and R.sub.2 respectively denote a linear or branched alkyl group having 1-18 carbon atoms capable of including one or non-neighboring two or more methylene groups which can be replaced with at least one species of --O--, --S--, --CO--, --COO--, --OCO-- and --OCOO--; ##STR2## and n is 0 or 1.

Abstract: An optically active compound represented by the following formula (I): ##STR1## wherein R.sub.1 denotes a linear or branched alkyl group having 1-18 carbon atoms optionally including one or non-neighboring two or more methylene groups which can be replaced with --X-- or ##STR2## with the proviso that X denotes O or S and Y denotes halogen; R.sub.2 denotes a linear alkyl group having 4-8 carbon atoms: and C* denotes an optically active asymmetric carbon atom. The mesomorphic compound is effective for providing a ferroelectric liquid crystal composition showing improved response characteristics and also effective for suppressing occurrence of reverse domain.

Abstract: A mesomorphic compound represented by the following formula (I): ##STR1## wherein R.sub.1 and R.sub.2 respectively denote an alkyl group having 1-16 carbon atoms capable of having a substituent; X.sub.1 and X.sub.2 respectively denote a single bond, ##STR2## and A.sub.1 and A.sub.2 respectively denote ##STR3## wherein X.sub.3 and X.sub.4 respectively denote hydrogen, fluorine, chlorine, bromine, --CH.sub.3, --CN or --CF.sub.3 ; and Z denotes --O-- or --S--.

Abstract: A mesomorphic compound represented by the following formula (I): ##STR1## wherein R.sub.1 denotes a linear or branched alkyl group having 2-16 carbon atoms capable of including one or two non-neighboring methylene groups which can be replaced with ##STR2## and capable of including fluorine substituted for hydrogen; A denotes --A.sub.1 -- or --A.sub.1 --A.sub.2 -- and B denotes --B.sub.1 -- or --B.sub.1 --B.sub.2 -- wherein A.sub.1, A.sub.2, B.sub.1 and B.sub.2 respectively denote ##STR3## wherein Y.sub.1 and Y.sub.2 respectively denote H, F, Cl, Br, --CH.sub.3, --CN or --CF.sub.3 ; Z.sub.1 and Z.sub.2 respectively denote ##STR4## Z.sub.3 denotes ##STR5## R.sub.2, R.sub.3 and R.sub.4 respectively denote a linear or branched alkyl group having 1-16 carbon atoms including a methylene group which can be replaced with ##STR6## with proviso that it is not adjacent to the silicon atom; p and q are respectively 0 or 1 with proviso that p+q is 0 or 1; and n is an integer of 1-12.

Abstract: A ferroelectric chiral smectic liquid crystal composition, comprising at least one compound represented by the following formula (I): ##STR1## wherein, R.sub.1 denotes a linear or branched alkyl group having 1-18 carbon atoms capable of having a substituent; R.sub.2 denotes a linear alkyl group having 1-12 carbon atoms; X.sub.1 denote a single bond, --O--, ##STR2## respectively denote ##STR3## and at least one compound represented by the following formula (II): ##STR4## wherein R.sub.3 and R.sub.4 respectively denote a linear or branched alkyl group having 1-18 carbon atoms capable of having a substituent; X.sub.2 and X.sub.3 respectively denote a single bond, --O--, ##STR5## and m and n are respectively 0, 1 or 2 with proviso that m+n is 2 or above.

Abstract: A ferroelectric chiral smectic liquid crystal composition, comprising at least one compound represented by the following formula (I): ##STR1## wherein R.sub.1 denotes a linear or branched alkyl group having 1-18 carbon atoms capable of having a substituent, R.sub.2 denotes a linear or branched alkyl group having 1-14 carbon atoms capable of having a substituent; X.sub.1 and X.sub.2 respectively denote a single bond, --O--, ##STR2## m is 0-7; and n is 0 or 1; and at least one compound represented by the following formula (II): ##STR3## wherein R.sub.3 and R.sub.4 respectively denote a linear or branched alkyl group having 1-18 carbon atoms capable of having a substituent; X.sub.3 and X.sub.4 respectively denote a single bond, --O--, ##STR4## Y.sub.1 denotes --CH.sub.2 O-- or --OCH.sub.2 --; and p and q are respectively 1 or 2.

Abstract: A mesomorphic compound represented by the following formula (I): ##STR1## wherein R.sup.1 and R.sup.2 respectively denote a linear or branched alkyl group having 3-18 carbon atoms capable of including one or more methylene groups which can be replaced with at least one species of ##STR2## with the proviso that --O-- cannot directly be connected to --O--, and R.sup.2 can also be halogen, --CN or --CF.sub.3 ; X denotes ##STR3## --CH.sub.2 O-- or --OCH.sub.2 ; A denotes ##STR4## and m and n are respecitvely 0 or 1 with the proviso that m+n=0 or 1. The mesomorphic compound is effective for providing a ferroelectric liquid crystal composition showing an improved low-temperature operation characteristic and a decreased temperature-dependence of response speed.